Method for Driving a Pump Device

ABSTRACT

During switchover from a suctioning step to a discharging step, a mixing pump ( 1 ) carries out a correcting step for displacing a displacing member ( 17 ) in the direction for reducing an internal volume of a pump chamber ( 2 ); and during switchover from the discharging step to the suctioning step, the pump carries out a correcting step for displacing a displacing member ( 17 ) in the direction for increasing the internal volume of the pump chamber ( 2 ). In the correcting step, intake ports ( 30   a,    30   b ), and discharging ports ( 40   a,    40   b ) of the pump chamber ( 2 ) are closed, and the displacing member ( 17 ) undergoes displacement for increasing or reducing the internal volume of the pump chamber ( 2 ) in a hermetic state. Instability caused by backlash of the displacing member ( 17 ) drive system can be eliminated, and a pressure difference between the pump chamber ( 2 ) interior and the fluid intake end or the fluid discharge end can be eliminated. It is therefore possible to eliminate or reduce variability in the amount of fluid intake or amount of fluid discharge when switching between the suctioning step and the discharging step.

TECHNICAL FIELD

The present invention relates to a method for driving a pump device suchas a diaphragm pump, which suctions fluid form its intake port anddischarges fluid from its discharge port by casing displacement of adisplacing member defining a part of a pump chamber.

BACKGROUND ART

One mixing pump device known in the art for mixing a plurality of fluidsin prescribed proportions is an apparatus designed to suction aplurality of fluids into a single pump chamber, mix them in the pumpchamber to form a mixed fluid, then discharge the mixed fluid from thepump chamber. Patent Citation 1 discloses a mixing pump device in ahigh-performance liquid chromatography device, for suctioning in andmixing several types of solvents with a plunger pump, and dischargingthe mixed fluid obtained thereby to the column.

The mixing pump device disclosed therein is designed to transmitrotation of a stepping motor to the plunger via a cam mechanism,increasing or decreasing the internal volume of the pump chamber. In thefluid suctioning step, during expansion of the pump chamber, valvespositioned on each of two inflow passages communicating with the pumpchamber are opened in sequence, and the fluids are suctioned via theinflow passages into the pump chamber where they are mixed.Subsequently, a discharge process is carried out, constricting the pumpchamber and discharging the mixed liquid.

[Patent Citation 1] JP 3117623 B

However, with a mixing pump device of this design, during switchoverfrom the discharging step to the suctioning step, a pressuredifferential may arise between the internal pressure of the pumpchamber, and the pressure on the inflow passages currently partitionedoff by the valves. Where such a pressure differential exists, if a valvethat was closed is then opened, there will be a temporary backflow offluid, the intake of the two types of fluid drawn into the pump chambervia the inflow passages will change, and their mixture ratio willfluctuate.

In the case of diaphragm pumps, a “non-responsive zone,” in which pumpchamber volume is unchanged despite deformation, is observed at theoutset of deformation by the diaphragm. Consequently, with a mixing pumpdevice that employs a diaphragm pump, during switchover from thedischarging step to the suctioning step or switchover from thesuctioning step to the discharging step, a delay will occur in thechange in the internal volume of the pump chamber. In addition, therewill be variation in the fluid intake to the pump chamber and in thefluid discharge from the pump chamber.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a method for driving apump device able to eliminate instability of the fluid intake operationand fluid discharge operation during switching between the dischargingstep and the suctioning step.

In order to solve the aforementioned problem, the method for driving apump device of the present invention comprises a suctioning step forsuctioning a fluid into a pump chamber from an intake port by inducingdisplacement of a displacing member that defines part of an insideperipheral surface of the pump chamber in the direction of increasinginternal volume of the pump chamber, with the discharge port of the pumpchamber closed and the intake port open; a discharging step fordischarging the fluid from the pump chamber by inducing displacement ofthe displacing member in the direction of decreasing internal volume ofthe pump chamber, with the discharge port open and the intake portclosed; and a correcting step for inducing displacement of thedisplacing member with both the intake port and the discharge port ofthe pump chamber closed. The steps are carried out in the order ofsuctioning, correcting, and discharging; or in the order of discharging,correcting, and suctioning.

With the method of the present invention, a correcting step is executedsubsequent to completion of the discharging step, followed thereafter byswitchover to the suctioning step. Alternatively, a correcting step isexecuted subsequent to completion of the suctioning step, followedthereafter by switchover to the discharging step. In the correctingstep, since the displacing member undergoes displacement while theintake port and the discharge port are closed, an increase or decreasein the internal volume of the pump chamber occurs in a hermetic state,and the internal pressure of the pump chamber changes in associationtherewith. Consequently, through appropriate setting of the direction ofdisplacement and the displacement level of the displacing member, it ispossible to eliminate the difference between the internal pressure ofthe pump chamber and the pressure on the fluid discharge end of thedischarge port. In the case of a diaphragm pump, since displacement ofthe diaphragm can be brought about by changing the internal pressure ofthe pump chamber, in the subsequent suctioning step or discharging step,it will be possible to change the internal volume of the pump chamberwith accurate response to displacement of the diaphragm. It isaccordingly possible to eliminate or reduce the extent of variation inthe fluid intake or fluid discharge during switchover between thesuctioning step and the discharging step.

Here, where the suctioning step and the discharging step are performedalternately, the correcting step will preferably be carried out bothduring switchover from the suctioning step to the discharging step, andduring switchover from the discharging step to the suctioning step.

In the correcting step executed between the suctioning step and thedischarging step, it is possible for example to induce displacingmovement of the displacing member in the direction for reducing theinternal volume of the pump chamber; and in the correcting step executedbetween the discharging step and the suctioning step, conversely, toinduce displacement of the displacing member in the direction forincreasing the internal volume of the pump chamber.

In order to eliminate the pressure differential inside and outside thepump chamber at initiation of the discharging step, in the correctingstep executed between the suctioning step and the discharging step,displacement of the displacing member is induced so as to eliminate thedifference between the internal pressure of the pump chamber and thepressure on the fluid discharge flow passage communicating with thedischarge port. In order to eliminate the pressure differential insideand outside the pump chamber at initiation of the suctioning step, inthe correcting step executed between the discharging step and thesuctioning step, displacement of the displacing member is induced so asto eliminate the difference between the internal pressure of the pumpchamber and the pressure on the fluid intake flow passage communicatingwith the intake port.

In this case, during the correcting step executed between the suctioningstep and the discharging step, the difference between the internalpressure of the pump chamber and the pressure on the fluid dischargeflow passage communicating with the discharge port can be monitored, anddisplacement of the displacing member induced on the basis of theresults of the monitoring. Similarly, during the correcting stepexecuted between the discharging step and the suctioning step, thedifference between the internal pressure of the pump chamber and thepressure on the fluid intake flow passage communicating with the intakeport can be monitored, and displacement of the displacing member inducedon the basis of the results of the monitoring.

Rather than performing closed loop control for monitoring the pressure,it is possible to carry out open loop control whereby during thecorrecting step, displacement of the displacing member is induced inaccordance with a predetermined condition.

Next, in the event that a plurality of fluids of different type are tobe taken in and mixed, a plurality of the intake ports may be formed inthe pump chamber; and during the suctioning step, an intake operationinvolving sequentially opening the closed plurality of intake ports andtaking in fluid is performed repeatedly, forming a mixed fluid in whichthe different types of fluids are mixed in predetermined proportions.

In this case, in preferred practice, before the fluid with the smallestmixture proportion is delivered into the pump chamber, at least somefluid having a larger mixture proportion than that fluid will bedelivered into the pump chamber. By having fluids with large intakelevels so delivered over several cycles, the fluids can be thoroughlymixed within the pump chamber.

Next, where fluids delivered into the pump chamber are to be distributedto different points, a plurality of the discharge ports may be formed inthe pump chamber; and during the discharging step, the closed pluralityof discharge ports may be opened sequentially and the fluid discharged.

The actuating method of the present invention is effective whenimplemented in a pump device constituted with a diaphragm pump in whichthe displacing member is a diaphragm. By inducing displacement of thediaphragm in the correcting step executed prior to initiation of thesuctioning step or prior to initiation of the discharging step, theinternal volume of the pump chamber can be increased or decreased withaccurate response to displacement of the diaphragm during the suctioningstep or the discharging step, whereby the fluid intake operation and thefluid discharge operation can be carried out properly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a conceptual diagram showing the basic configuration of amixing pump device embodying the present invention;

FIG. 2A and FIG. 2B are respectively a timing chart depicting operationof the mixing pump device shown in FIG. 1, and a descriptive diagramdepicting the relationship of the position of the piston to resolution;

FIGS. 3A to 3D are descriptive diagrams relating to deformation of adiaphragm;

FIG. 4 is a conceptual diagram showing the basic configuration of amixing pump device embodying the present invention;

FIG. 5A and FIG. 5B are respectively a perspective view of a mixing pumpdevice embodying the present invention, and a descriptive diagramshowing the flow passages thereof in plan view;

FIG. 6 is an exploded perspective view of the mixing pump device of FIG.5, viewed from diagonally above;

FIG. 7 is a descriptive diagram showing in cross section theconfiguration of the mixing pump device of FIG. 5A;

FIG. 8 is an exploded perspective view of the mixing pump device of FIG.5A, shown divided on the vertical;

FIG. 9A and FIG. 9B are respectively a descriptive diagram of the pumpchamber in a state of expanded internal volume, and the pump chamber ina state of contracted internal volume, in the mixing pump device of FIG.8;

FIGS. 10A to 10C are respectively a perspective view, a plan view, and asectional view of a rotor employing the rotating body of the pumpmechanism shown in FIG. 8;

FIGS. 11A to 11C are respectively a perspective view, a plan view, and asectional view of a moving body employing the rotating body of the pumpmechanism shown in FIG. 8;

FIG. 12 is a descriptive diagram of the principal parts of a valve usedfor the active valves 5, 6 of the mixing pump device embodying theinvention, shown cut along the axis and viewed from diagonally above;and

FIG. 13 is a descriptive diagram of the lines of magnetic force of thevalve shown in FIG. 12.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be described hereinbelow with reference tothe accompanying drawings.

FIG. 1 is a conceptual diagram showing the basic configuration of amixing pump device embodying the present invention. As illustrated inFIG. 1, the mixing pump device 1 has a pump chamber 2. In the pumpchamber 2 there are formed a plurality (two, in this example) of intakeports 30 a, 30 b; and a plurality (two, in this example) of dischargeports 40 a, 40 b. The intake ports 30 a, 30 b communicate respectivelywith inflow passages 3 a, 3 b; and the discharge ports 40 a, 40 bcommunicate respectively with outflow passages 4 a, 4 b. The pump devicemain unit 7 is made up of the pump chamber 2, the intake ports 30 a, 30b, the discharge ports 40 a, 40 b, the inflow passages 3 a, 3 b, and theoutflow passages 4 a, 4 b.

Inflow-side active valves 5 a, 5 b for individually opening and closingthe intake ports 30 a, 30 b are disposed in these ports. Outflow-sideactive valves 6 a, 6 b for individually opening and closing thedischarge ports 40 a, 40 b are disposed in these ports. Theseinflow-side active valves 5 a, 5 b and outflow-side active valves 6 a, 6b are opened and closed by means of a control unit 18.

A portion of the inside peripheral surface of the pump chamber 2 isdefined by a displacing member 17 such as a piston or diaphragm. Thedisplacing member 17 is displaceable in the outward and inward directionof the pump chamber; in the present example, the displacing member 17undergoes displacement by means of a drive unit 105 equipped with astepping motor 12. The pump drive mechanism 13 is composed of thisdisplacing member 17 and drive unit 105. When the stepping motor 12 ofthe drive unit 105 turns in one direction, the displacing member 17 isdisplaced in the direction A of increasing internal volume of the pumpchamber 2; and when the stepping motor 12 turns in the oppositedirection, the displacing member 17 is displaced in the direction B ofdecreasing internal volume of the pump chamber 2.

During the suctioning step of the mixing pump device 1 of this design,for example, with one inflow-side active valve 5 a open, and with theother inflow-side active valve 5 b and the outflow-side active valves 6a, 6 b closed by the control unit 18, the displacing member 17 undergoesdisplacement towards direction A by means of the drive unit 105, therebysuctioning a fluid LB into the pump chamber 2 from the inflow passage 3b via the intake port 30 b. Next, by switching the open/closed states ofthe inflow-side active valves 5 a, 5 b and displacing the displacingmember 17 further towards direction A, another fluid LA is suctionedinto the pump chamber 2 from the inflow passage 3 a via the intake port30 a. The fluids. LA, LB are mixed within the pump chamber 2.

During the discharging step of the mixing pump device, for example, withone outflow-side active valve 6 a open, and with the other outflow-sideactive valve 6 b and the inflow-side active valves 5 a, 5 b closed bythe control unit 18, the displacing member 17 undergoes displacementtowards direction B via the drive unit 105, thereby discharging themixed fluid from the pump chamber 2 into the outflow passage 4 a via thedischarge portion 40 a. By switching the open/closed states of theoutflow-side active valves 6 a, 6 b and displacing the displacing member17 further towards direction B, the mixed fluid can be discharged to theoutflow passage 4 b from the other discharge port 40 b.

In this mixing pump device 1, a correcting step, discussed below, isexecuted in the interval between the suctioning step and the dischargingstep.

FIGS. 2A and 2B are respectively a timing chart depicting operation ofthe mixing pump device shown in FIG. 1, and a descriptive diagramdepicting the relationship of the position of the displacing member toresolution. The operation of the mixing pump device 1 will be describedin detail with reference to FIG. 2A. In the description hereinbelow, theproportion of inflow (mixture proportion) of the first fluid LA and thesecond fluid LB taken in via the two inflow passages 3 a, 3 b is assumedto be 1:5.

In FIG. 2A, the uppermost level shows the intake operation and dischargeoperation by the pump drive mechanism 13; the intake operation by thepump drive mechanism 13 is accomplished, for example, by clockwiserotation of the stepping motor 12 displacing the displacing member 17 inthe direction A of increasing the internal volume of the pump chamber 2(see FIG. 1). The discharge operation by the pump drive mechanism 13 isaccomplished, for example, by counterclockwise rotation of the steppingmotor 12 displacing the displacing member 17 in the direction B ofdecreasing the internal volume of the pump chamber 2 (see FIG. 1). Thepump drive mechanism 13 is halted via suspending the power supply to thestepping motor 12.

The inflow-side active valves 5 a, 5 b and the outflow-side activevalves 6 a, 6 b all assume the open state once a positive pulse has beeninput, switching to the closed state at the point in time that anegative pulse is input. Once a negative pulse has been input, thevalves assume the closed state once a positive pulse has been input,switching to the open state at the point in time that a negative pulseis input.

In FIG. 2A, first, at time t1, power to the stepping motor 12 issuspended, and the pump drive mechanism 13 comes to a stop. At time t1,all of the active valves 5 a, 5 b, 6 a, 6 b are in the closed state.

In this state, at time t1, of the two inflow-side active valves 5 a, 5b, only the inflow-side active valve 5 b located in the inflow passage 3b which corresponds to the liquid LB is switched to the open state.Next, at time t2, power is supplied to the stepping motor 12, and thestepping motor 12 rotates clockwise displacing the displacing member 17in the direction A of increasing the internal volume of the pump chamber2. As a result, the liquid LB flows into the pump chamber 2 from theinflow passage 3 b. At time t3 following input of a 125-step pulse tothe stepping motor 12, power to the stepping motor 12 is suspended, andthe displacing member 17 comes to a halt as well. At the same time, theinflow-side active valve 5 b is switched from the open state to theclosed state. As a result, the flow of the liquid LB into the pumpchamber 2 from the inlet passage 3 b halts. According to this intakeoperation, one-half of the total inflow amount of the liquid LB is drawninto the pump chamber 2.

Next, at time t4, only the inflow-side active valve 5 a is switched tothe open state; and at time t5 power is supplied to the stepping motor12, and the stepping motor 12 rotates in the same direction (clockwise)displacing the displacing member 17 in the same direction (the directionA of increasing the internal volume of the pump chamber 2). As a result,the liquid LA flows into the pump chamber 2 from the inflow passage 3 a.Then, at time t6 following input of a 50-step pulse to the steppingmotor 12, power to the stepping motor 12 is suspended, and thedisplacing member 17 comes to a halt as well. At the same time, theinflow-side active valve 5 a is switched from the open state to theclosed state. As a result, the flow of the liquid LA into the pumpchamber 2 from the inlet passage 3 a halts. According to this intakeoperation, the total inflow amount of the liquid LA is drawn into thepump chamber 2.

Next, at time t7, the inflow-side active valve 5 b only is againswitched to the open state, and at time t8 power is supplied to thestepping motor 12, whereupon the stepping motor 12 rotates in the samedirection (clockwise). The displacing member 17 is thereby displacedfurther in the same direction (the direction of increasing the internalvolume of the pump chamber 2), and the fluid LB flows into the pumpchamber 2 from the inlet passage 3 b. Then, at time t9 following inputof a 125-step pulse to the stepping motor 12, power to the steppingmotor 12 is suspended, and the displacing member 17 comes to a halt aswell. At the same time, the inflow-side active valve 5 b is switchedfrom the open state to the closed state. As a result, the flow of theliquid LB into the pump chamber 2 from the inlet passage 3 b halts.According to this intake operation, the remaining one-half of the totalinflow amount of the liquid LB is drawn into the pump chamber 2.

After completion of the suctioning step in the above manner, during timet10 and time t11, the correcting step is executed, followed byswitchover to the discharging step. The correcting step will bediscussed later; first, a description of the discharging step startingat time t11 shall be provided.

At time t11, of the two outflow-side active valves 6 a, 6 b, only theoutflow-side active valve 6 a is switched to the open state; at timet12, power is supplied to the stepping motor 12, and the stepping motor12 rotates in the opposite direction (counterclockwise direction). Thedisplacing member 17 is thereby displaced in the direction B ofdecreasing the internal volume of the pump chamber 2, and the mixedliquid in the pump chamber 2 is discharged into the outflow passage 4 a.Then, at time t13 following input of a 150-step pulse to the steppingmotor 12, power to the stepping motor 12 is suspended, and thedisplacing member 17 comes to a halt as well. At the same time, theoutflow-side active valve 6 a is switched from the open state to theclosed state. As a result, the mixed liquid is discharged from theoutflow passage 4 a, in an amount equivalent to one-half the liquid thathas flowed into the pump chamber 2. Subsequently, during time t17 andtime t18, the correcting step is executed, and the operation concludes.

Next, at time t14, of the two outflow-side active valves 6 a, 6 b, onlythe outflow-side active valve 6 b is switched to the open state; at timet15, power is supplied to the stepping motor 12, and the stepping motor12 rotates in the same direction (counterclockwise direction),displacing the displacing member 17 further in the direction B ofdecreasing the internal volume of the pump chamber 2, and dischargingthe mixed liquid in the pump chamber 2 into the outflow passage 4 b.Then, at time t16 following input of a 150-step pulse to the steppingmotor 12, power to the stepping motor 12 is suspended, and thedisplacing member 17 comes to a halt. At the same time, the outflow-sideactive valve 6 b is switched from the open state to the closed state. Asa result, the mixed liquid is discharged from the outflow passage 4 b,in an amount equivalent to one-half the liquid that has flowed into thepump chamber 2. Subsequently, during time t17 and time t18, thecorrecting step is executed, and the operation concludes.

The correcting step which is performed during the interval of time t10to t11 and during the interval of time t17 to t18 will now be described.At points in time of switchover of the direction of displacement of thedisplacing member 17, specifically, at top dead center during switchoverfrom the suctioning step to the discharging step, and at bottom deadcenter during switchover from the discharging step to the suctioningstep, there is a tendency for resolution of positioning to be low, asshown in FIG. 2B. In the case where a gear mechanism is used as thedrive unit 105 for example, this tendency could be caused by backlash.The displacing member 17 is also susceptible to delayed response tooperation and slipping out of position at top dead center and bottomdead center.

Particularly where a diaphragm is employed as the displacing member 17,delayed response to displacement tends to occur at top dead center andbottom dead center, where the direction of displacement of the diaphragmchanges. Also, the shape of the diaphragm is susceptible to a pressuredifference between the internal pressure of the pump chamber 2 andatmospheric pressure. This point shall be discussed with reference toFIGS. 3A to 3D.

Where, for example, the internal pressure of the pump chamber 2 is equalto atmospheric pressure as illustrated in FIG. 3A, the diaphragm 170will not experience any unintended displacement due to a pressuredifference. Where the internal pressure of the pump chamber 2 is greaterthan atmospheric pressure as illustrated in FIG. 3B, the diaphragm 170becomes distended due to the pressure difference. Conversely, where theinternal pressure of the pump chamber 2 is lower than atmosphericpressure as illustrated in FIG. 3C, the diaphragm 170 becomesconstricted by the equivalent of the pressure difference.

Consequently, when the pump chamber 2 is at negative pressure uponcompletion of the suctioning step at time t9, the diaphragm will tend toassume the condition depicted in FIG. 3C. Or, when the pump chamber 2 isat positive pressure upon completion of the discharging step at timet16, the diaphragm will tend to assume the condition depicted in FIG.3B. Thus, if in the condition depicted in FIG. 3C, the outflow-sideactive valve 6 a is opened at time t11 and the pump chamber 2 nowcommunicates with the outflow passage 4 a to the outflow port 40 a endthereof with respect to the valve 6 a, there is a risk that the mixedfluid in the outflow passage 4 a on the outflow port 40 a end thereofwill backflow into the pump chamber 2 due to the differential head. Ifsuch a condition occurs, the discharged amount of the mixed liquid willbe less than the intended amount. If in the condition depicted in FIG.3B, the inflow-side active valve 5 b is opened at time t1 and the pumpchamber 2 now communicates with the inflow passage 3 b to the outflowinflow port 30 b end thereof with respect to the valve 5 b, the mixedliquid in the pump chamber 2 will backflow from the inflow passage 3 b,and the inflowing amount of the second liquid LB will be less than theintended amount.

Meanwhile, even in instances where the pump chamber 2 is at a pressureequal to atmospheric pressure upon completion of the suctioning step attime t9 or upon completion of the discharging step at time t16, aproblem such as is described hereunder may occur where the outflowpassages 4 a, 4 b are situated above and the inflow passages 3 a, 3 bare situated below as depicted in FIG. 3D. First, upon completion of theintake at time t9, since the pressure of the pump chamber 2 equals thepressure to the outside of the inflow-side active valve 5 b, when theoutflow-side active valve 6 a is opened at time t11 and the pump chamber2 communicates with the outflow port 40 a end of the outflow passage 4a, there is a risk that the fluid mixed at the outflow port 40 b via thevalve 6 a of the outflow passage 4 a will flow back into the pumpchamber 2 due to the differential head. If such a condition occurs, thediaphragm 170 will become distended prior to actuation of the diaphragm170, and the discharged amount of the mixed liquid will be less than theintended amount. Also, even where the pump chamber 2 is at a pressureequal to atmospheric pressure upon completion of the discharging step attime t16, after completion of the discharging step at time t16, sincethe pressure of the pump chamber 2 equals the pressure to the outside ofthe outflow-side active valve 6 b, when during the second intake cyclethe inflow-side active valve 5 b is opened at time t1 and the pumpchamber now communicates with the inflow port 30 b end of the inflowpassage 3 b, there is a risk that the mixed liquid will backflow throughthe inflow passage 3 b. If such a condition occurs, the diaphragm 170will become indented prior to actuation of the diaphragm 170, and theinflow amount of the liquid LB will be less than the intended amount.

In order to avoid such adverse effects, a correcting step for thepurpose of correcting the position of the displacing member 17 isexecuted during switchover from the suctioning step to the dischargingstep, and during switchover from the discharging step to the suctioningstep. During switchover from the suctioning step to the dischargingstep, the displacing member 17 undergoes displacement to a slight extentin the direction for reducing the internal volume of the pump chamber 2,whereas during switchover from the discharging step to the suctioningstep the displacing member 17 undergoes displacement to a slight extentin the direction for increasing the internal volume of the pump chamber2.

Turning now to a more detailed description, as shown in FIG. 2A, duringtime t10 to time t11 after completion of intake and prior to initiatingdischarge, power is supplied to the stepping motor 12, which rotates inthe counterclockwise direction, displacing the displacing member 17 inthe direction of decreasing the internal volume of the pump chamber 2.Conversely, during time t17 to time t18 after completion of dischargeand prior to initiating intake, power is supplied to the stepping motor12 which rotates in the clockwise direction, displacing the displacingmember 17 in the direction of increasing the internal volume of the pumpchamber 2.

In this correcting step, the valves 5 a, 5 b, 6 a, 6 b and thedisplacing member 17 can be actuated under control by the control unit18, in accordance with preestablished conditions.

It is also possible to employ a method wherein during changeover fromintake to discharge, and during changeover from discharge to intake, thepressure difference between locations to either side of the valves 5 b,6 a that switch from the open state to the closed state is monitoredeither directly or indirectly; and during the correcting step, based onthe monitoring results, the displacing member 17 is displaced in thedirection eliminating the pressure difference.

Direct monitoring of the pressure difference between locations to eitherside of the valves 5 b, 6 a may be accomplished by positioning pressuresensors in the pump chamber 2, at a location in the inflow passage 3 bto the outside of the valve 5 b, and at a location in the outflowpassage 4 a to the outside of the valve 6 a, and detecting pressuredifference on the basis of detection results of these pressure sensors.Indirect monitoring of the pressure difference between locations toeither side of the valves 5 b, 6 a may be accomplished by measuring theheight location of the outflow port 40 a of the outflow passage 4 a, andmonitoring the level of the second liquid LB shown in FIG. 3D.

In the mixing pump device 1 discussed above, when the stepping motor 12turns in a first direction the displacing member 17 undergoesdisplacement in the direction for increasing the internal volume of thepump chamber 2, and when the stepping motor 12 turns in the oppositedirection, the displacing member 17 undergoes displacement in thedirection for reducing the internal volume of the pump chamber 2.Consequently, irrespective of the position of the displacing member 17,during the interval that the stepping motor 12 is turning in the firstdirection, a plurality of fluids can be suctioned into the pump chamber2 in prescribed proportions simply by closing the active valves 6 a, 6 bpositioned on the outflow passages 4 a, 4 b, and sequentially openingand closing the active valves 5 a, 5 b positioned on the inflow passages3 a, 3 b. Then, during the interval that the stepping motor 12 isturning in the opposite direction, the mixed fluid can be dischargedfrom the pump chamber 2 simply by closing the active valves 5 a, 5 bpositioned on the inflow passages 3 a, 3 b, and opening one or both ofthe active valves 6 a, 6 b positioned on the outflow passages 4 a, 4 b.Thus, unlike a mechanism which transmits rotation of the stepping motor12 to the displacing member 17 via a cam mechanism, there is no need tomonitor cam position with a photointerrupter or the like. It istherefore possible to simplify the design of the mixing pump device 1,and make it smaller and less expensive.

It is a simple matter to modify the extent of displacement stroke of thedisplacing member 17 by varying the signal pattern presented to thestepping motor 12. A resultant advantage is that the extent ofdisplacement stroke of the displacing member 17 can be set appropriatelydepending on the type of liquids being used.

The control unit 18 controls opening and closing of the active valves 5a, 5 b, 6 a, 6 b in such a way that, of the first liquid LA and thesecond liquid LB which inflow from the inflow passages 3 a, 3 b, aportion of the second liquid LB having the larger mixture proportionflows into the pump chamber 2 prior to suctioning in the first liquid LAhaving the smaller mixture proportion. It is therefore possible toprevent the first liquid LA from becoming unevenly distributed in acorner of the pump chamber 2, e.g. in proximity to the active valve 5 a,so as to achieve thorough mixing of the first liquid LA and the secondliquid LB. In particular, more thorough mixing of the first liquid LAand the second liquid LB can be achieved because an amount equivalent toone-half of the total amount of the second liquid LB having the largermixture proportion is suctioned into the pump chamber 2, then the firstliquid LA having the smaller mixture proportion is suctioned into thepump chamber 2, and finally the remaining one-half of the second liquidLB is suctioned into the pump chamber 2.

The correcting step is executed during the interval from time t10 totime t11, and during the interval from time t17 to time t18. Even wherethe displacing member 17 has reached top dead center or bottom deadcenter, it will return from the top dead center or bottom dead centerand perform intake or discharge. Accuracy of the intake amount anddischarge amount is accordingly high. Particularly where the displacingmember 17 is a diaphragm, during switchover from the discharging step tothe suctioning step, or during switchover from the suctioning step tothe discharging step, there is a tendency for displacement to occur in anon-responsive condition in which the internal volume of the pumpchamber does not change despite deformation of the diaphragm, and forthere to be variation in the intake amount and discharge amount. Byinterposing the correcting step, such variability can be eliminated.

Furthermore, where a diaphragm is employed as the displacing member 17,a pressure differential between the internal pressure of the pumpchamber 2 and atmospheric pressure can produce unwanted deformation ofthe diaphragm. Since intake and discharge are carried out aftercorrecting such deformation by executing the correcting step, accuracyof the intake amount and discharge amount is high.

[Specific Configuration Example of the Mixing Pump Device]

Next, a specific configuration example of a mixing pump device embodyingthe present invention will be described.

First, the basic design of the mixing pump device to be discussedhereinbelow shall be described with reference to FIG. 4 in order toreduce the level of complexity. Since the basic design of the mixingpump device of the present example is the same as that of the mixingpump 1 depicted in FIG. 1, corresponding parts have been assignedidentical symbols in the drawing.

As shown in FIG. 4, the pump device main unit 7 of the mixing pumpdevice 1A of the present example has a pump chamber 2, two inflowpassages 3 a, 3 b communicating with the pump chamber 2, and six outflowpassages 4 a through 4 f communicating with the pump chamber 2. The twoinflow passages 3 a, 3 b and the six outflow passages 4 a through 4 fcommunicate mutually independently with the pump chamber 2. Inflow-sideactive valves 5 a, 5 b are positioned respectively on the two inflowpassages 3 a, 3 b. Outflow-side active valves 6 a through 6 f arepositioned respectively on the six outflow passages 4 a through 4 f.

The pump drive mechanism 13 has a diaphragm 170 that defines a portionof the inside peripheral surface of the pump chamber 2; a drive unit 105equipped with a stepping motor 12 for displacing this diaphragm 170; anda control unit 18 for controlling opening and closing of the inflow-sideactive valves 5 a, 5 b and the outflow-side active valves 6 a through 6f.

Next, FIG. 5A and FIG. 5B are respectively a perspective view and a planview of the mixing pump device 1A. FIG. 6 is an exploded perspectiveview thereof; and

FIG. 7 is a descriptive diagram showing the configuration thereof incross section.

Reference to these drawings is made in the description providedhereunder. The mixing pump device 1A has pipes defining intake ports 30a, 30 b and discharge ports 40 a through 40 f connected to one face 71of the pump device main unit 7 which is in the shape of a box. The pumpdevice main unit 7 has a stacked structure composed, in order, of acircuit board 74 for the pump drive mechanism 13 and the active valves 5a, 5 b, 6 a through 6 f; a bottom plate 75; a base plate 76; a flowpassage formation plate 77 having formed thereon flow passages ofchannel shape to be described later; a sealing sheet 78 for sealing offthe upper sides of the flow passages via covering the upper face of theflow passage formation plate; and an upper plate 79 to which theaforementioned pipes are connected.

Holes 137, 67 a through 67 h providing installation spaces for the pumpdrive mechanism 13 and for the active valves 5 a, 5 b, and 6 a through 6f are formed in the base plate 76. A round through-hole 21 constitutingthe pump chamber 2 is formed at a central location in the flow passageformation plate 77; and around this through-hole 21, on the lower faceof the flow passage formation plate 77, are formed recesses (not shown)constituting the valve chambers of the active valves 5 a, 5 b, 6 athrough 6 f Eight channels 41 a through 41 h extend radially out fromthe through-hole 21. Additional channels 42 a, 42 b . . . , etc. areformed in proximity to the channels 41 a through 41 h of the flowpassage formation plate 77.

The inflow passages 3 a, 3 b and the outflow passages 4 a through 4 fare formed by the eight channels 41 a through 41 h. Specifically, whenthe base plate 76, the flow passage formation plate 77, and the sealingsheet 78 are stacked, the inflow passages 3 a, 3 b and the outflowpassages 4 a through 4 f are formed by the channels 41 a through 41 f,42 a, 42 b . . . ; and the inflow-side active valves 5 a, 5 b and theoutflow-side active valves 6 a through 6 f are positioned in theindividual inflow passages 3 a, 3 b and outflow passages 4 a through 4f.

Since the active valves 5 a, 5 b, 6 a through 6 f are positioned in aplane around the pump chamber 2, the flow passages in the individualinflow passages 3 a, 3 b and the outflow passages 4 a through 4 f areshort, and the mixing pump device 1A can have a thin profile.Additionally, since variation in the amount discharged from the outflowpassages 4 a through 4 f can be minimized, fluids can be dischargedaccurately in the proper amounts. Moreover, the length of the flowpassage from the pump chamber 2 to the outflow-side active valves 6 athrough 6 f is the same in each of the plurality of outflow passages 4 athrough 4 f. Thus, outflow amounts via the outflow passages 4 a through4 f can be controlled with high accuracy. Furthermore, since the inflowports 30 a, 30 b and the outflow ports 40 a through 40 f open onto thesame surface 71 of the pump device main unit 7, external connection ofthe mixing pump device 1A is a simple matter. Moreover, since the pumpdevice main unit 7 is furnished with a flow passage formation plate 77having inflow passages 3 a, 3 b and outflow passages 4 a through 4 fformed in the shape of a channel on one face thereof, and with a sealingsheet 78 that is positioned juxtaposed against this one face, amultitude of flow passages can be formed in a compact pump device mainunit 7, and the mixing pump device 1A can be manufactured efficiently aswell.

Furthermore, the two inflow passages 3 a, 3 b and the six outflowpassages 4 a through 4 f have mutually identical design; and theinflow-side active valves 5 a, 5 b and the outflow-side active valves 6a through 6 f have mutually identical design. Consequently, any of theinflow passages 3 a, 3 b and the outflow passages 4 a through 4 f can beutilized as the inflow passages 3 a, 3 b or the outflow passages 4 athrough 4 f. Consequently, [the mixing pump device] is not limited totwo types of liquid, but can be used to mix and discharge three or moretypes of liquid.

(Detailed Design of the Pump Drive Mechanism)

The pump drive mechanism 13 which is incorporated into the mixing pumpdevice 1A will be described with reference to FIGS. 8 to 11. FIG. 8 isan exploded perspective view of the mixing pump device 1A, shown dividedon the vertical. FIG. 9A and FIG. 9B are [respectively] a descriptivediagram of the pump chamber in the expanded state, and the pump chamberin the contracted state. FIGS. 10A to 10C are respectively a perspectiveview, a plan view, and a sectional view of a rotor employing therotating body of the pump mechanism shown in FIG. 8. FIGS. 11A to 11Care respectively a perspective view, a plan view, and a sectional viewof a moving body employing the rotating body of the pump mechanism shownin FIG. 8.

As shown in FIGS. 8 and 9A, the pump drive mechanism 13 is furnishedgenerally with a diaphragm 170 that functions as the displacing memberfor taking in and discharging liquid by expanding and contracting thepump chamber 2 communicating with the inflow passages 3 a, 3 b and theoutflow passages 4 a through 4 f; and a drive unit 105 for driving thediaphragm 170.

The drive unit 105 is furnished with an annular stator 120; a rotatingbody 103 disposed coaxially to the inside of this stator 120; a movingbody 160 disposed coaxially to the inside of this rotating body 103; anda conversion mechanism 140 for converting rotation of the rotating body103 to motion of the moving body 160 in the axial direction. The driveunit 105 is installed between the bottom plate 75 and the base plate 76,within a space formed in the base plate 76.

The stator 120 has a structure including a two-level stack of units eachcomposed of a coil 121 wound around a bobbin 123, and a pair of yokes125 positioned so as to cover the coil. In the each of two units in theupper and lower levels, the pole teeth which project in the axialdirection from the inside peripheral edges of the pair of yokes 125 arearrayed in alternating fashion in the circumferential direction.

As shown in FIGS. 8, 9 and 10A through 10C, the rotating body 103 has acup-shaped member 130 open at the top, and an annular rotor magnet 150attached to the outside peripheral face of a cylindrical-shaped rotatingbody 103 drum portion 131 of the cup-shaped member 130. In the center ofthe floor 133 of the cup-shaped member 130 there is formed a recess 135recessed upwardly in the axial direction; on the bottom plate 75 thereis formed a bearing portion 751 adapted to receive a ball 118 that ispositioned within the recess 135. An annular shoulder portion 766 isformed on the inside rim of the upper edge of the base plate 76. At theupper end portion of the cup-shaped member 130, an annular shoulderportion which faces towards the annular shoulder portion 766 on the baseplate 76 is formed by the upper edge of the drum portion 131 and anannular flange 134. The annular space defined by these annular shoulderportions accommodates a bearing 180 which is composed of an annularretainer 181 and ball bearings 182 held at locations spaced apart in thecircumferential direction by the retainer 181. In this way, the rotatingbody 103 is supported rotatably about the axis on the pump device mainunit 7.

The outside peripheral face of the rotor magnet 150 faces towards thepole teeth which are lined up in the circumferential direction along theinside peripheral face of the stator 120. On the outside peripheral faceof the rotor magnet 150, S poles and N poles are lined up in alternatingfashion in the circumferential direction, with the stator 120 and thecup-shaped member 130 constituting the stepping motor.

As shown in FIGS. 8, 9, and 11A through 11C, the moving body 160 has afloor 161, a cylindrical portion 163 projecting out in the axialdirection from the center of the floor 161, and a drum portion 165 ofcylindrical shape formed so as to surround this cylindrical portion 163;a male thread 167 is formed on the outside periphery of the drum portion165.

In order to constitute the conversion mechanism 140 for bringing aboutreciprocating movement of the moving body 160 in the axial direction bymeans of rotation of the rotating body 103, as shown in FIGS. 8, 9, 10Athrough 10C, and 11A through 11C, a female thread 137 is formed at fourlocations spaced apart in the circumferential direction, on the insideperipheral face of the drum portion 165 of the cup-shaped member 130.The male thread 167, which engages with the female thread 137 andconstitutes a power transmission mechanism 141, is formed on the outsideperipheral face of the drum portion 165 of the moving body 160.Consequently, the moving body 160 is supported to the inside of thecup-shaped member 130, with the moving body 160 positioned to the insideof the cup-shaped member 130 so that the male thread 167 meshes with thefemale thread 137.

On the floor 161 of the moving body 160 there are formed through-holesconstituting six slots 169 along the circumferential direction;meanwhile, six projections 769 extend from the base plate 76, with thelower ends of the projections 769 fitting into the slots 169 andconstituting a co-rotation preventing mechanism 149. Specifically,during rotation of the cup-shaped member 130, the moving body 160 isprevented from rotating by the co-rotation preventing mechanism 149composed of the projections 769 and the slots 169; therefore, rotationof the cup-shaped member 130 will be transmitted to the moving body 160via the power transmission mechanism 141 composed of the female thread137 and the male thread 167 of the moving body 160, as a result of whichthe moving body 161 undergoes linear movement to one side or the otherin the axial direction, depending on the direction of rotation of therotating body 103.

(Configuration of Displacing Member)

Referring back to FIGS. 8 and 9A, the diaphragm 170 is linked directlyto the moving body 160. The diaphragm 170, which is cup-shaped, has afloor 171; a drum portion 173 of cylindrical shape rising up in theaxial direction from the outside peripheral edge of the floor 171; and aflange portion 175 spreading towards the outside periphery from theupper end of this drum portion 173. The diaphragm, with the centerportion of the floor 171 thereof covering the cylindrical portion 163 ofthe moving body 160, is secured in place from above and below by afastening screw 178 and a cap 179. The outside peripheral edge of theflange portion 175 of the diaphragm 170 is constituted by a thicksection, which is adapted to ensure liquid-tightness, and also functionsas a positioning section. The thick section is secured in place betweenthe base plate 76 and the flow passage formation plate 77, around thethrough-hole 21 of the flow passage formation plate 77. In this way, thediaphragm 170 defines the lower face of the pump chamber 2, and assuresliquid-tightness between the base plate 76 and the flow passageformation plate 77 around the pump chamber 2.

The drum portion 173 of the diaphragm 170 doubles back in a U shapedcross section, with the doubled back portion 172 thereof changing shapedepending on the position of the moving body 160. The doubled backportion 172 having a U shaped cross section of the diaphragm 170 ispositioned within a space of annular shape defined between a first wallface 168 composed of the outside peripheral face of the cylindricalportion 163 of the moving body, and a second wall face 768 composed ofthe inside peripheral faces of the projections 769 extended from thebase plate 76. Consequently, with the diaphragm in any of the statesshown in FIG. 9A or 9B, or during the process of moving between thestates shown in these drawings, the doubled back portion 172 ofdiaphragm 170, while remaining retained within the annular space,undergoes deformation so as to expand or roll up along the first wallface 168 and the second wall face 768.

As shown in FIGS. 8, 9A, and 10A through 10C, a single groove 136 isformed on the floor 133 of the cup-shaped member 130 over an angularrange of 270° in the circumferential direction, while a projection 166is formed facing downward from the bottom face of the moving body 160.Here, the moving body 160 does not rotate about the axis but does movein the axial direction, while the rotating body 103 does rotate aboutthe axis but does not move in the axial direction. Consequently, theprojection 166 and the groove 136 function as a stopper for regulatingthe stop position of the rotating body 103 and the moving body 160.Specifically, the groove 136 changes in depth in the circumferentialdirection; as the moving body 160 moves downward in the axial directionthe projection 166 will engage within the groove 136, and upon rotationof the rotating body 103, the edge of the groove 136 will come intoabutment with the projection 166. As a result, the rotating body 103will be prevented from rotating, thus regulating the stop position ofthe rotating body 103 and the moving body 160, i.e. the position ofmaximum expansion of the internal volume of the diaphragm 170.

(Operation of the Pump Drive Mechanism)

In the pump drive mechanism 13 of such a design, when power is suppliedto the coil 121 of the stator 120, the cup-shaped member 130 rotates,and this rotation is transmitted to the moving body 160 via theconversion mechanism 140. Consequently, the moving body 160 undergoeslinear reciprocating motion in the axial direction. As a result, thediaphragm 170 deforms in association with the motion of the moving body160, causing the pump chamber 2 to expand or contract, whereby theinflow of liquid from the inflow passages 3 a, 3 b and the dischargingof liquid to the outflow passages 4 a through 4 f take place in the pumpchamber 2. During this time, the doubled back portion 172 of diaphragm170, while remaining retained within the annular space, undergoesdeformation so as to expand or roll up along the first wall face 168 andthe second wall face 768, so no unnecessary sliding motion occurs.Moreover, even if the diaphragm 170 is subjected to pressure from thefluid in the pump chamber 2, the diaphragm is restricted both inside andout within the annular space, and thus will not deform. Furthermore, thelower position of the moving body 160 is restricted by the stoppercomposed of the groove 136 of the cup-shaped member 130 and theprojection 166 of the moving body 160. Thus, the diaphragm 170 undergoesdisplacement with high accuracy, in association with the rotation of thecup-shaped member 130. In the drive unit 105, when the stepping motorrotates in one direction, the diaphragm 170 is displaced the directionof increasing the internal volume of the pump chamber 2; and when thestepping motor rotates in the other direction, the diaphragm 170 isdisplaced the direction of decreasing the internal volume of the pumpchamber 2.

As discussed above, in the pump drive mechanism 13, rotation of therotating body 103 by the stepping motor mechanism is transmitted to themoving body 160 via the conversion mechanism 140 which utilizes thepower transmission mechanism 141 composed of the male thread 167 and thefemale thread 137, causing the moving body 160 to which the diaphragm170 is fastened to undergo reciprocating linear motion. Thus, power istransmitted from the drive unit 105 to the diaphragm 170 by the minimumnumber of components needed to do so, whereby the pump drive mechanism13 can be made smaller, thinner, and less expensive. Moreover, by givingthe male thread 167 and the female thread 137 in the power transmissionmechanism 141 a smaller lead angle, or by increasing the number of poleteeth of the stator on the drive end, it is possible for the moving body160 to be advanced in very small increments. Consequently, the volume ofthe pump chamber 2 can be finely controlled, so metered discharge can becarried out with high accuracy.

Furthermore, the doubled back portion 172 of diaphragm 170, whileremaining retained within the annular space, undergoes deformation so asto expand or roll up along the first wall face 168 and the second wallface 768, so no unnecessary sliding motion occurs. Consequently, nounnecessary load is produced, and the diaphragm 170 will have a longerlife. Moreover, even if the diaphragm 170 is subjected to pressure fromthe fluid in the pump chamber 2, it will not deform. Therefore, the pumpdrive mechanism 13 can carry out metered discharge with high accuracy,and reliability is high as well.

Moreover, since the rotating body 103 is rotatably supported about theaxis on the pump device main unit 7 via the ball bearings 182, slidingloss is minimal, and the rotating body 103 is held stably in the axialdirection, stabilizing the thrust in the axial direction. It istherefore possible to make the drive unit 105 smaller, improvedurability, and improve discharging ability.

While threads were employed for the power transmission mechanism 141 ofthe conversion mechanism 140, it is also possible to employ a cammechanism instead. Furthermore, while a cup-shaped diaphragm has beenused, a diaphragm of some other shape, or a piston equipped with anO-ring, can be used instead.

The numbers of intake ports and discharge ports may be different fromthose described hereinabove. Furthermore, while the sealing sheet 78 forsealing off the upper face and the upper plate 79 to which the pipes areconnected are formed by separate components, an arrangement thatdispensed with the pipes of the upper plate 79 and provides only outflowholes to the sealing sheet 78, for connection via seal members wouldalso be possible.

(Configuration of Active Valves)

FIGS. 12 and 13 are, respectively, a descriptive diagram of theprincipal parts of a valve used for the active valves 5 a, 5 b and theactive valves 6 a through 6 f of the mixing pump device 1A, shown cutalong the axis and viewed from diagonally above; and a descriptivediagram of the lines of magnetic force thereof.

As shown in the drawings, the active valves 5 a, 5 b (hereinafterdenoted as active valves 5) and the active valves 6 a through 6 f(hereinafter denoted as active valves 6) are provided with a linearactuator 201 positioned in the holes 57, 67 a through 67 h of the baseplate 76; this linear actuator 201 has a stationary body 203 having acylindrical shape, and a moveable body 205 having a round rod shapepositioned inside the stationary body 203. The stationary body 203 has acoil 233 wound in annular configuration onto a bobbin 231; and astationary body yoke 235 running around both sides of the coil in theaxial direction from the outside peripheral face of the coil 233, withone distal edge 236 a and the other distal edge 236 b thereof facing inthe axial direction across a slit 237, to the inside peripheral side ofthe coil 233. The movable body 205 has a first movable body yoke 251having a disk shape, and a pair of magnets 253 a, 253 b stacked oneither side of the first movable body yoke 251 in the axial direction.For the pair of magnets 253 a, 253 b it is possible to use Nd—Fe—B orSm—Co rare earth magnets, or resin magnets. In the movable body 205, asecond movable body yoke 255 a, 255 b is stacked on each of the pair ofmagnets 253 a, 253 b, on the end face thereof on the opposite side fromthe first movable body yoke 251.

The pair of magnets 253 a, 253 b are each magnetized in the axialdirection, and oriented with the same pole facing the direction of thefirst movable body yoke 251. Here, the pair of magnets 253 a, 253 b aredescribed as oriented with the N pole of each facing the direction ofthe first movable body yoke 251, and the S pole of each facing towardsthe outside in the axial direction; however, the direction ofmagnetization could be reversed.

The outside peripheral face of the first movable body yoke 251 protrudesout beyond the outside peripheral faces of the pair of magnets 253 a,253 b. Likewise, the outside peripheral faces of the second movable bodyyokes 255 a, 255 b protrude out beyond the outside peripheral faces ofthe pair of magnets 253 a, 253 b.

Recesses are formed in each axial end of the first movable body yoke251, and the pair of magnets 253 a, 253 b are fitted respectively intothese recesses and secured there with adhesive or the like. It isacceptable to employ any arrangement in which the first movable bodyyoke 251, the pair of magnets 253 a, 253 b, and the second movable bodyyokes 255 a, 255 b are fastened through unification by an adhesive,press-fitting, or a combination of these.

Bearing plates 271 a, 271 b (bearing members) are fastened in openingsat either axial end of the stationary body 203, and spindles 257 a, 257b which project out to either side in the axial direction from thesecond movable body yokes 255 a, 255 b are each slidably inserted intoholes in the bearing plates 271 a, 271 b. In this way, the movable body205 is supported on the stationary body 203 so as to be capable ofreciprocating motion in the axial direction. In this state, the movablebody 205 faces the inside peripheral face of the stationary body 203across a prescribed gap, with the distal edges 236 a, 236 b of thestationary body yoke 235 facing one another in the axial directionwithin the gap between the outside peripheral face first movable bodyyoke 251 and the inside peripheral face of the coil 233. A gap ismaintained between the moveable body 205 and the stationary body yoke235 as well. It is acceptable to employ any arrangement in which thesecond movable body yokes 255 a, 255 b and the spindles 257 a, 257 b arefastened through unification by an adhesive, press-fitting, or acombination of these.

In the linear actuator 201 of the design described above, for the periodthat electrical current, on the right side when facing the drawing, isflowing through the coil 233 towards the viewer from the far side and,on the left side facing the drawing, is flowing away from the viewer andtowards the far side, the lines of magnetic force will be as depicted inFIG. 13. Accordingly, the moveable body 5 is first subjected to thrustand moves in the axial direction due to Lorentz force, as indicated byarrow A. On the other hand, when the direction of current through thecoil 233 reverses, the moveable body 205 will descend along the axialdirection as indicated by arrow B.

In the linear actuator 201, the moveable body 205 is propelled bymagnetic force, and a frustoconically shaped coil spring 291 ispositioned as an urging member between the bearing plate 271 a and thesecond movable body yoke 255 a, on one side in the axial direction.Consequently, the moveable body 205 descends while deforming thecompression spring; and as the moveable body 205 moves at high speedwhen ascending, assisted by the shape recovery force of the compressionspring.

In the linear actuator 201 designed in this manner, the center portionof a diaphragm valve 260 positioned in the valve chamber 270 (recess 68a through 68 h) is connected to the end of one of the spindles 257 b. Anannular thick section 261 providing liquid-tightness and a positioningfunction is formed on the outside periphery of the diaphragm 260; theoutside peripheral section of the diaphragm 260 including this annularthick section 261 is held between the base plate 76 and the flow passageformation plate 77, ensuring liquid-tightness.

The displacing member is not limited to a diaphragm 260, it beingpossible to employ a bellows valve or some other valve instead. Anarrangement in which the spindles 257 a, 257 b and the displacing memberare separate components connected together, or an arrangement in whichthe spindles 257 a, 257 b and the displacing member are formedintegrally, is acceptable.

As discussed above, the pair of magnets 253 a, 253 b in the moveablebody 205 are oriented with identical poles facing one another, producingmagnetic repulsive force, but since the first movable body yoke 251 ispositioned between the magnets 253 a, 253 b, the pair of magnets 253 a,253 b can be secured oriented with identical poles facing one another.

Also, since the pair of magnets 253 a, 253 b in the moveable body205[are oriented] with identical poles facing the first movable bodyyoke 251, strong magnetic flux is generated in the radial direction fromthe first movable body yoke 251. Accordingly, where the peripheral facesof the first movable body yoke 251 and the coil 233 are juxtaposed, themoveable body 205 can be imparted with strong thrust.

Since the magnets 253 a, 253 b need only be magnetized in the axialdirection, in contrast to the case where the magnets 253 a, 253 b aremagnetized in the radial direction, magnetization is a simple mattereven where the magnets are small, which is suitable for mass productionpurposes.

Moreover, since the outside peripheral face of the first movable bodyyoke 251 protrudes out beyond the outside peripheral faces of the pairof magnets 253 a, 253 b, the magnetic attracting force acting in theaxial direction and the perpendicular direction on the moveable body 205can be minimized, even if the stationary body yoke 235 is provided.Similarly, since the outside peripheral faces of the second movable bodyyokes 255 a, 255 b protrude out beyond the outside peripheral faces ofthe pair of magnets 253 a, 253 b, the magnetic attracting force actingin the axial direction and the perpendicular direction on the moveablebody 205 can be minimized, even when the stationary body yoke 235 isprovided. The assembly operation is facilitated and the moveable bodyresists tilting, which are advantages obtained as a result.

Since the magnets 253 a, 253 b are positioned at the outside peripheryside in the coil 33, the magnets 253 a, 253 b can be smaller, and theactive valves 5, 6 may be designed less expensively, as compared to whenthe magnets 253 a, 253 b are positioned outwardly from the coil 233.Also, since the coil 233 is positioned to the outside, the magnetic pathcan be closed with the stationary yoke only.

Furthermore, in the stationary body 203, since the bearing plates 271 a,271 b for supporting the spindles 257 a, 257 b so as to be moveable inthe axial direction are held in openings that open in the axialdirection, there is no need for separate bearing members. An additionaladvantage is that since the bearing plates 271 a, 271 b can be securedon the basis of the stationary body 203, the spindles 257 a, 257 b willnot tilt.

[Applications of the Mixing Pump Device]

The mixing pump device embodying the present invention can be used, forexample, for a direct methanol fuel cell (hereinafter DMFC) that takesprotons directly from methanol in order to generate electricity. Thiskind of DMFC has a generating unit having a electromotive portion(cell), and a liquid feed pump for pumping a methanol aqueous solution.The cell is composed of an anode (fuel electrode) having an anodecollector and an anode catalyst layer; a cathode (air electrode) havinga cathode collector and a cathode catalyst layer; and an electrolytemembrane positioned between the anode and the cathode. The methanolaqueous solution is delivered to the anode by the liquid feed pump,while air is delivered to the cathode by an air pump or blower.

Accordingly, by employing the mixing pump device embodying the presentinvention as the liquid feed pump, it is possible to appropriately mixmethanol with water, methanol with a methanol aqueous solution, amethanol aqueous solution with methanol, or a methanol aqueous solutionwith another methanol aqueous solution, and to supply the cell with amethanol aqueous solution of adjusted methanol concentration. At theanode of the cell, which is the electromotive portion of the DMFC,methanol oxidation activity is low, with associated voltage loss.Voltage loss occurs at the cathode as well. Thus, the output drawn froma single cell is very low, so the DMFC employs a plurality of cells inorder to generate a prescribed output. In such instances as well, themixing pump device 1A embodying the present invention can be used todeliver methanol aqueous solution of adjusted methanol concentration toeach cell.

Applications of the mixing pump device embodying the present inventionare not limited to fuel cells. The mixing pump device can be used as apump for blending a plurality of chemical solutions in order to blend acompound chemical. It can also be used as a refrigerator icemaker pump,for discharging from outflow paths sherbets of different color andflavor for each icemaker block.

OTHER EMBODIMENTS

While the preceding embodiment focused on the example of using adiaphragm 170 as the displacing member 17, the invention can instead beembodied in a mixing pump device of a type using a plunger as thedisplacing member. Also, while the preceding embodiment was an exampledesigned with a plurality of outflow passages, the invention can insteadbe embodied in a mixing pump device having a single outflow passage.

In the preceding embodiment, the invention was embodied in a mixing pumpdevice, but the invention can also be embodiment in a metering pump fordischarging a single type of liquid.

1. A method for driving a pump device, comprising: a suctioning step forsuctioning a fluid into a pump chamber from an intake port by inducingdisplacement of a displacing member that defines part of an insideperipheral surface of the pump chamber in the direction of increasinginternal volume of the pump chamber, with the discharge port of the pumpchamber closed and the intake port open; a discharging step fordischarging the fluid from the pump chamber by inducing displacement ofthe displacing member in the direction of decreasing internal volume ofthe pump chamber, with the discharge port open and the intake portclosed; and a correcting step for inducing displacement of thedisplacing member with both the intake port and the discharge port ofthe pump chamber closed; wherein the steps are carried out in the orderof suctioning, correcting, and discharging; or in the order ofdischarging, correcting, and suctioning.
 2. The method for driving apump device of claim 1 wherein the suctioning and discharging steps areperformed alternatingly, with the correcting step therebetween.
 3. Themethod for driving a pump device of claim 1 wherein the displacingmember is subjected to a displacing movement in the direction forreducing the internal volume of the pump chamber in the correcting stepexecuted between the suctioning and discharging steps; and thedisplacing member is subjected to a displacing movement in the directionfor increasing the internal volume of the pump chamber in the correctingstep executed between the discharging and suctioning steps.
 4. Themethod for driving a pump device of claim 1 wherein the displacingmember is subjected to a displacing movement so as to eliminate thedifference between an internal pressure of the pump chamber and apressure on the fluid discharge flow passage communicating with thedischarge port in the correcting step executed between the suctioningand discharging steps; and the displacing member is subjected to adisplacing movement so as to eliminate the difference between theinternal pressure of the pump chamber and the pressure on the fluidintake flow passage communicating with the intake port in the correctingstep executed between the discharging and suctioning steps.
 5. Themethod for driving a pump device of claim 4 wherein the differencebetween the internal pressure of the pump chamber and the pressure inthe fluid discharge flow passage communicating with the discharge portis monitored, and the displacing member is displaced on the basis of theresults of the monitoring in the correcting step executed between thesuctioning and discharging steps; and the difference between theinternal pressure of the pump chamber and the pressure on the fluidintake flow passage communicating with the intake port is monitored, andthe displacing member is displaced on the basis of the results of themonitoring in the correcting step executed between the discharging andsuctioning steps.
 6. The method for driving a pump device of claim 4wherein during the correcting step, the displacing member is displacedin accordance with a predetermined condition.
 7. The method for drivinga pump device of claim 1 wherein a plurality of the intake ports areformed in the pump chamber; and during the suctioning step, a suctioningoperation involving sequentially opening the closed plurality of intakeports and drawing in fluid is performed repeatedly, forming a mixedfluid in which the different types of fluids are mixed in predeterminedproportions.
 8. The method for driving a pump device of claim 7 whereinbefore the fluid with the smallest mixture ratio is taken into the pumpchamber, at least some fluid having a larger mixture proportion than theaforementioned fluid is taken into the pump chamber.
 9. The method fordriving a pump device of claim 1 wherein a plurality of the dischargeports are formed in the pump chamber; and the closed plurality ofdischarge ports are opened sequentially and the fluid is dischargedduring the discharging step.
 10. The method for driving a pump device ofclaim 1 wherein the displacing member is a diaphragm.